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Physics/Magnet powered rail gun


QUESTION: My question is about a similar device to the following:

The device I thinking of is a simple device using several angled magnets on either side of a rail. The device accelerates a steel ball from rest to certain velocity when it is placed at one end of the 'gun' .

Does the working of the device depend on the initial speed of the steel ball - at which speed it is rolled into the device?

This will lead to a follow up question..

ANSWER: Of course it depends on the initial velocity of the ball.  You'd have to give me a lot more detail about the strength of the magnets and the makeup of the balls and so on for that device to make the least little bit of sense.

---------- FOLLOW-UP ----------

QUESTION: I apologize for not being more specific.

What I meant was, that if the exit speed from the permanent magnet rail gun is 3 m/s for example, does it make a difference if the steel ball is rolled into the device at different speeds, that is, for example walking speed, 1.6 m/s approximately, or 0.1 m/s or 0.001 m/s or any speed in between? Will the exit speed vary ?

Basically I am asking how tolerant the device is to input speeds of the steel ball - will it the steel ball simply stop in its tracks because the input speed is too high or too low?

The device I am talking about is best represented by this image:

ANSWER: The image page you sent me to has dozens of rail guns on it, so that really wasn't helpful.  It should not matter too much what the input speed of your projectile is, really, as long as the entry time coincides with whatever you're using to power it.  Are you using an electrical pulse? If you're just using some arrangement of permanent magnets or something then it's not really a classical rail gun.  It really isn't clear which type of gun you're trying to build...

---------- FOLLOW-UP ----------

QUESTION: The rail gun I am referring to is the one on the top of the page. I am referring to an arrangement of permanent magnets.

Without moving the permanent magnets, I don't see how you add energy to the ball in question.  But for any Gauss/rail gun your final velocity should be largely determined by the structure itself and not at all by the input velocity at such low energies compared to the final energy.


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Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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